Kalam Haroon, Fontana Mary F, Kumar Dhiraj
Cellular Immunology Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
PLoS Pathog. 2017 Mar 3;13(3):e1006236. doi: 10.1371/journal.ppat.1006236. eCollection 2017 Mar.
Transcriptional reprogramming of macrophages upon Mycobacterium tuberculosis (Mtb) infection is widely studied; however, the significance of alternate splicing (AS) in shaping cellular responses to mycobacterial infections is not yet appreciated. Alternate splicing can influence transcript stability or structure, function and localization of corresponding proteins thereby altering protein stoichiometry and physiological consequences. Using comprehensive analysis of a time-series RNA-seq data obtained from human macrophages infected with virulent or avirulent strains of Mtb, we show extensive remodeling of alternate splicing in macrophage transcriptome. The global nature of this regulation was evident since genes belonging to functional classes like trafficking, immune response, autophagy, redox and metabolism showed marked departure in the pattern of splicing in the infected macrophages. The systemic perturbation of splicing machinery in the infected macrophages was apparent as genes involved at different stages of spliceosome assembly were also regulated at the splicing level. Curiously there was a considerable increase in the expression of truncated/non-translatable variants of several genes, specifically upon virulent infections. Increased expression of truncated transcripts correlated with a decline in the corresponding protein levels. We verified the physiological relevance for one such candidate gene RAB8B; whose truncated variant gets enriched in H37Rv infected cells. Upon tweaking relative abundance of longer or shorter variants of RAB8B transcripts by specialized transduction, mycobacterial targeting to lysosomes could be promoted or blocked respectively, which also resulted in corresponding changes in the bacterial survival. Our results show RAB8B recruitment to the mycobacterial phagosomes is required for phagosome maturation. Thus the abundance of truncated RAB8B variant helps virulent Mtb survival by limiting the RAB8B levels in the cells, a mechanism which we subsequently verified in human primary macrophages. Taken together we demonstrate alternate splicing as a new locus of intervention by Mtb and provide attractive alternative to exploit for novel drug targets against Mtb.
结核分枝杆菌(Mtb)感染后巨噬细胞的转录重编程已得到广泛研究;然而,可变剪接(AS)在塑造细胞对分枝杆菌感染反应中的重要性尚未得到重视。可变剪接可影响转录本稳定性或相应蛋白质的结构、功能及定位,从而改变蛋白质化学计量和生理后果。通过对从感染有毒或无毒Mtb菌株的人类巨噬细胞获得的时间序列RNA测序数据进行综合分析,我们发现巨噬细胞转录组中的可变剪接发生了广泛重塑。这种调控的全局性很明显,因为属于运输、免疫反应、自噬、氧化还原和代谢等功能类别的基因在感染巨噬细胞中的剪接模式有显著差异。感染巨噬细胞中剪接机制的系统性扰动很明显,因为参与剪接体组装不同阶段的基因在剪接水平上也受到调控。奇怪的是,几种基因的截短/不可翻译变体的表达显著增加,特别是在有毒感染时。截短转录本表达的增加与相应蛋白质水平的下降相关。我们验证了一个这样的候选基因RAB8B的生理相关性;其截短变体在感染H37Rv的细胞中富集。通过专门的转导调整RAB8B转录本较长或较短变体的相对丰度后,分枝杆菌分别可以被促进或阻止靶向溶酶体,这也导致了细菌存活的相应变化。我们的结果表明,RAB8B募集到分枝杆菌吞噬体是吞噬体成熟所必需的。因此,截短的RAB8B变体的丰度通过限制细胞中的RAB8B水平来帮助有毒Mtb存活,我们随后在人类原代巨噬细胞中验证了这一机制。综上所述,我们证明可变剪接是Mtb的一个新的干预位点,并为开发抗Mtb的新型药物靶点提供了有吸引力的选择。